A turbo charger comprises a turbine connected to a compressor. By means of the compressor ambient air is sucked in, compressed to a higher pressure and fed to an engine. Exhaust gas of the engine is led to the turbine, where the exhaust gas is expanded for driving the compressor. For controlling the pressure of the sucked in ambient air a bypass for bypassing the turbine is provided, so that the turbine can be operated by a reduced exhaust gas flow. The bypass is opened and closed by a so called waste gate. The waste gate can be actuated by the pressure of a duty cycle, for instance by means of the ambient air pressure after the compressor. The waste gate is spring loaded in closing direction. Due to the spring force a minimum boost pressure is necessary for opening the waste gate, wherein this minimum boost pressure is named “basic boost pressure”. Turbocharger boost pressure control can only be performed above the basic boost pressure, since only above the basic boost pressure the opening and the closing of the waste gate can be controlled. Since the basic boost pressure limits the possibilities of the control, the basic boost pressure is an important factor for providing a good control of the turbo charger. For that reason it is important to know the basic boost pressure with a high accuracy. But the basic boost pressure depends on ambient air conditions, which can not be calculated in advance.
It is known to provide a table of a set of values of the basic boost pressure at standard conditions and to provide further tables for correcting the provided basic boost pressure values to ambient conditions. For that reason a further table for providing a correction factor based on an ambient air temperature T and a further table for providing a correction factor based on an ambient air pressure p are provided.
It is a disadvantage of such kind of a control method that these tables have to be derived by a calibration by means of a plurality of experiments at different ambient air temperatures and different ambient air pressures, which requires a high effort leading to high costs.
It is at least one object of the invention to provide a method of operating a turbo charger as well as a controller, by which it is possible to control the turbo charger on the basis of a basic boost pressure, which is received with high accuracy in a simplified manner. Furthermore, other objects, desirable features, and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.